Open (non-enclosed) magnets for magnetic resonance imaging

Abstract

An open magnet having two magnet assemblies arranged in a spaced-apart, parallel relationship to define a working space therebetween is provided for magnetic resonance imaging. Each assembly has an annular superconductive coil and a ferromagnetic field enhancer encircled by the superconductive coil. The field enhancers are substantially cylindrical ferromagnetic pole pieces which are encircled by a respective one of the superconductive coils. The magnet assemblies are attached to a C-shaped support frame which is rotatively mounted to a pedestal member. The frame can thus be rotated between vertical and horizontal imaging positions. The field enhancers are shaped so as to maximize homogeneity in the imaging volume while keeping their weight and volume to a minimum. The specific shape of the field enhancers is determined with a nonlinear optimization design method.

What is claimed is: 
     
       1. A magnet assembly comprising: a superconductive coil; and   a ferromagnetic field enhancer disposed adjacent to said superconductive coil, said ferromagnetic field enhancer comprising a first cylindrical portion, a second cylindrical portion having a greater diameter than said first cylindrical portion, and a frustoconical portion joining said first and second cylindrical portions, said ferromagnetic field enhancer having a recessed end face formed on said second cylindrical portion.   
     
     
       2. The magnet assembly of claim 1 wherein said first cylindrical portion has an end face with a conical recess formed therein. 
     
     
       3. The magnet assembly of claim 1 wherein said first cylindrical portion has an end face with a plurality of annular grooves formed therein. 
     
     
       4. The magnet assembly of claim 3 wherein said grooves are of varying depths. 
     
     
       5. An open magnet device comprising: first and second superconductive coils;   a first ferromagnetic field enhancer encircled by said first superconductive coil; and   a second ferromagnetic field enhancer encircled by said second superconductive coil, each one of said first and second ferromagnetic field enhancers comprising a first cylindrical portion, a second cylindrical portion having a greater diameter than said first cylindrical portion and a recessed end face formed thereon, and a frustoconical portion joining said first and second cylindrical portions, said first and second field enhancers being spaced apart from and parallel to one another so as to define a working volume therebetween.   
     
     
       6. The open magnet device of claim 5 further comprising a support frame which supports said field enhancers in a spaced-apart, parallel relationship. 
     
     
       7. The open magnet device of claim 6 further comprising a pedestal member to which said support frame is rotatively mounted. 
     
     
       8. The open magnet device of claim 5 wherein said first cylindrical portion has an end face with a conical recess formed therein. 
     
     
       9. The open magnet device of claim 5 wherein said first cylindrical portion has an end face with a plurality of annular grooves formed therein. 
     
     
       10. The open magnet device of claim 9 wherein said grooves are of varying depths. 
     
     
       11. The magnet assembly of claim 1 wherein said superconductive coil encircles said first cylindrical portion. 
     
     
       12. The open magnet device of claim 5 wherein said first superconductive coil encircles said first cylindrical portion of said first field enhancer, and said second superconductive coil encircles said first cylindrical portion of said second field enhancer. 
     
     
       13. The open magnet device of claim 5 wherein said recessed end face of said first ferromagnetic field enhancer and said recessed end face of said second ferromagnetic field enhancer both face said working volume. 
     
     
       14. An open magnet device comprising: a pedestal;   a C-shaped frame rotatively mounted to said pedestal;   a first ferromagnetic field enhancer attached to one end of said C-shaped frame;   a second ferromagnetic field enhancer attached to another end of said C-shaped frame, each one of said first and second ferromagnetic field enhancers comprising a first cylindrical portion, a second cylindrical portion having a greater diameter than said first cylindrical portion and a recessed end face formed thereon, and a frustoconical portion joining said first and second cylindrical portions, said first and second field enhancers being spaced apart from and parallel to one another so as to define a working volume therebetween;   a first superconductive coil encircling said first ferromagnetic field enhancer; and   a second superconductive coil encircling said second ferromagnetic field enhancer.